Timing devices for rotary engines



Aug. 10, 1965 PERAS 3,199,495

TIMING DEVICES FOR ROTARY ENGINES Filed June 8, 1961 2 Sheets-Sheet 1 /N l/E N 7' 0/? L zwen Perms- B Y Mm am, M/ZZm/Z Aug. 10, 1965 L. PERAS 3,199,495

TIMING DEVICES FOR ROTARY ENGINES Filed June 8, 1961 2 Sheets-Sheet 2 INVENTOR Lucien Perms United States Patent C TIMING DEVICES FQR RGTARY ENGINES Lucien Pras, Biliancourt, Seine, France, assignor t Regie Nationale des Usines Renault, Billancourt, France Filed June 8, 1961, Ser. No. 115,809 Claims priority, application France, July 6, 1960, 832,246, Patent 1,269,802 1 Claim. (Cl. 123-8) This invention relates to a timing device for rotary engines of the type comprising fxed combustion chambers housed in the stator.

It should be remembered that in engines of this type the number of combustion chambers equals the number of contact points between the conjugate contours of the stator and rotor, this number of contact points corresponding to that of the stator lobes.

For a four-stroke operation an odd number of chambers must be provided, but this number is immaterial in a two-stroke engine. If inlet and exhaust valves are provided in these combustion chambers, they can be actuated either through a gear system operatively interconnecting with a proper gear ratio the engine shaft and a camshaft, or through a linkage system operatively interconnecting the rotor and the camshaft.

It is advantageous to avoid this auxiliary control systern and to provide a direct operative connection between the cams and the rotor.

Therefore, this invention is concerned with a direct timing system wherein the rotor comprises a cam of specific design co-acting with a roller and rocker device for actuating the valves.

However, as an eccentric motion is imparted to the rotor and to the rotor carrying shaft (called hereinafter the engine shaft), the cam must be made with a special contour.

it is another object of this invention to provide a cam having this specific contour for an engine of this type.

The low part of bottom portion of the cam, that is, the cam contour causing the valves to remain constantly seated, is defined by the path of the center of the timing roller connected to and engaging the valve concerned; this path is of curvilinear configuration and describes a cycloid. The same path becomes an epicycloid when the number of teeth of the rotor is lower than that of the stator, or an hypocycloid when the number of teeth of the rotor is greater than that of the stator. The number of arcs constituting this cyclcid is equal to the number of teeth of the rotor and the roller envelope is a curve parallel to this cycloid.

The valve lift is obtained by adding a swell or raised portion to this cam contour. The number of raised portions is half the tooth number in a four-stroke engine and the same in a two-stroke engine.

The angular location of the raised portion on the cycloidal contour varies as a function of the position of the roiler in relation to the combustion chamber of which it controls the valve.

The invention will now be described with reference to the attached drawings illustrating diagrammatically by way of example a five-chamber engine wherein the rotor contour is a four-arc shortened epicycloid, the cam bottom being likewise a four-arc epicycloid.

In the drawings:

FEGURE 1 shows in cross section a typical arrangement of an engine of this type;

FIGURE 2 is an axial section of the engine taken along line 2-2 of FIG. 1;

PEGURE 3 is a fragmentary diagrammatic section showing an alternate embodiment; and

FEGURES 4 and 5 are diagrams illustrating the method of determining the cam contour.

Referring to FIG. 1, the engine comprises a rotor 1 mounted on the eccentric portion 2 of shaft 3. The rotor revolves within a stator 4 comprising chambers 5 in which valves such as 6 are mounted.

According to this invention, a cam 7 for actuating the valves is mounted on the rotor. To this end, a rocker 8 fulcrumed on a pin 9 is actuated by a rod 10 having a roller ltla responsive to the contour of the cam 7, this contour being a cycloid and comprising swells 11 and troughs 12.

in the form of embodiment shown in FlGS. 1 and 2, another rocker is provided in the vicinity of the cam disk. The valve lift is controlledby the passage of the roller in the recesses of the epicycloid, and in this case the rod 16 is tension stressed.

In the alternate embodiment illustrated in FIG. 3, the valve disposal is of conventional character in that the rod it) is compression stressed, the valve 6 being unseated each time a cam swell engages the roller carried by this rod.

In order to afford a clear understanding of the shape to be given to the cam, the method of determining its contour will now be explained in connection with an en gine of the type illustrated, that is, having a four-tooth rotor revolving within a five-chamber stator (FIG. 4).

Let E be the eccentricity of the rotor in relation to its shaft.

Associated with this rotor is a circle 0, centered on I and having a radius 4E, this circle rolling without slip ping Within another, larger circle C centered at O, which has a radius 513 associated with the stator. Circle G in FIG. 4 corresponds to shaft 3 in PEG. 1 and circle F of FIG. 4 corresponds to a portion of shaft 2 of FIG. 1. As a result, when the crank arm OI is rotated through an angle a, which is the general term representing the rotation angles of the crank 01 and the rotor with respect to the stator, the rotor revolves about itself through an angle a/ 4. For the purpose of analysis, the center of circles F and C is considered stationary in FIG. 4, and the center of circles G and C is shown to move about circle F in FIG. 4. Therefore, circle C is considered to be rolling around rotor circle C in PEG. 4 but for the purpose of analysis.

Let A be the general center of a roller. The general term A is represented by A A A A A A for the valve closing positions and A A A g, A' A A for the valve opening positions (see FIG. 4). To trace its path in the rotor plane, from which the cam contour will be determined, it will be assumed that the rotor is fixed: thus, C becomes fixed and C revolves thereabout without slipping while carrying along the point A. It will be assumed firstly that this point A is in its inoperative position (corresponding to a seated valve). Its path in the rotor plane will be called the cam bottom or core; to draft same, 0 will be given several successive positions 0 O O located ,on the circle F centered at I and having a radius E. To a rotation a of 10 corresponds a [3/5 of 0A. By transferring the constant length 0A to the corresponding radii, the successive points of the path A A A A, will be obtained. This path will be a four-arc epicycloid. Five points such as A can be placed at the vertices of a regular pentagon centered at 0; they will generate the same path.

In the figure, the different positions of 0A are designated angularly by 0::(01, 0A), not by p:(lO 10) because ct is the angle of rotation of the crankshaft (crank arm 10) causing the point in question of the path to become coincident with the center of the roller. The angle of origin azO corresponds to a crank arm 01 directed toward the center of the roller. The positions of 0A are represented for the values of or equal 36, 72, 144 and OI means generally the line between points and I; (OI, 0A) means generally the angle between points IOA.

The curve giving the valve lift is constructed according to the following method:

Let us assume that in the stator the point A is movable, during its lift, along a stator radius. This is the case of a push-rod guided in a radial bore.

A lifting law illustrated in Cartesian ordinates in FIG. will be given as a function of the crank arm angle or.

The curve is obtained by transferring from the core contour on the radius GA the lifts corresponding to the angles: A A' zL L' A A zL L AzA gzLgL z' and so forth. Thus, a curve which is the locus of the roller centers is obtained. The cam proper is obtained by taking the envelope of the circles centered on A which are representative of the rollers.

The example described is a specific case wherein the maximum lift is obtained for a zero crank arm angle, that is, when the crank arm is directed toward the roller. It will be seen that this arrangement, combined with a certain proportion between the lift and the eccentricity (L being approximately equal to B) provides a particularly advantageous cam shape having a nearly rectilinear contour; to obtain the best conditions the trough of the epicycloid is used.

Although the present invention has been described in conjunction with preferred embodiments, it is-to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understood. Such modifications and variations are considered to be within the purview and scope of the invention and appended claim.

I claim:

Rotary engine comprising a stator including a pair of end walls and a peripheral wall joining said end walls and defining a hollow Working space, a rotating shaft lying along the axis of said Working space, an eccentric secured to said shaft, a rotor in said working space rotatably journalled on said eccentric and mounted eccentrically on said shaft, said outer rotor surface being formed with a plurality of lobes of cycloidal configuration, said stator peripheral wall being formed with a plurality of chambers of a shape generally conforming to the shape of said rotor lobes, said stator having one more chamber than said rotor has lobes, valves in each of said chambers of said stator, and means to cause the lifting of said valves, said means comprising a cam rigidly secured to said rotor and consequently having an eccentric movement identical to the movement of the rotor, and members, one for each valve, provided with rollers which rest against the surface of the cam, each of said members being operatively connected to its valve so as to impart a lifting movement to its valve, said cam having a basic contour of generally cycloidal form, said basic contour being such that as the engine and cam rotate, the dis tance between said rollers and said stator peripheral walls remains constant, said basic contour being increased at suitable points by protuberances by means of which said lifting movement is obtained.

References Cited by the Examiner UNITED STATES PATENTS 1,799,527 4/31 Plato 123-14 FOREIGN PATENTS 838,124 11/38 France. 850,935 9/39 France.

KARL J. ALBRECHT, Primary Examiner.

RALPH H. BRAUNER, JOSEPH H. BRANSON, JR.,

Examiners. 

